PLACE-CONSTANTS FOR ASTER PRENANTHOIDES. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY. 
LXIV. 
GEORGE HARRISON SHULL. 
(WITH EIGHTEEN FIGURES) 
I. INTRODUCTION. 
GEOGRAPHIC isolation has long been accredited as an important 
factor in the process of evolution, but with the introduction of methods 
calculated to demonstrate the evolutionary processes an altogether 
new conception has been gained regarding the importance of locality 
asa modifying factor. Statistical methods have shown that the organ- 
isms of any species from different stations, often quite near each other, 
ate not to be considered homogeneous, and that in order to establish 
* Proper basis for comparison investigations must deal with definite 
teas. The modal condition of any species .prevailing on such a 
limited area is known as a “place-mode” for that species at that 
place, : 
i importance of determining and recording place-modes for 
Yarlous ‘species was first emphasized by DaveNpoRT (18994); and 
: “*sponse to his appeal a considerable number of local statistical 
‘tudies have been made. Some of these studies have shown that 
ne determination of place-constants is not so simple a problem as 
a at first supposed. As a result of my earlier studies on Aster 
% oe catey it was shown that the establishment of place-constants 
* Species of Aster would involve the collection of all the heads 
ats during the sa canaasde since there is a continuous and are 
throu aed change in the variable characters from day to z 
tee : ~ season. It was suggested there that sige e 
Season “ might also be presented by the same population rom 
: season. The results of a number of studies on various 
iP te other investigators, both beforé and since my eres of 
ion Bows, lead to the same conclusion or admit of the same explana- 
ULE 1999 i 1895, MAacLEop 1899, LUDWIG 1901, TowER 1902, 
1904] EP OON I 9°93; REINOHL 1903, etc.). 
a 
